During recent years, traditional power grids have emerged as smart grids. Many aspects of future smart grids are defined in the SG3 standardization roadmap prepared by International Electro Technical Commission. The roadmap declares an efficient transmission and distribution network as one prime driver of a smart grid. It also urges the development of a stable communication link between various components of a power grid, which will enable overall grid monitoring and rapid troubleshooting at central control stations.
Overhead high voltage transmission lines are a vital mode of transportation of power for widely distributed transmission network. The overhead lines serve to connect generation units to distribution sites via high voltage transmission lines terminating at substations, and to connect generation units to end users via relatively low voltage distributed lines.
The overhead lines remain exposed to extreme conditions due to long distance transmission. Such exposure commonly results in reduction of ground clearance, in the form of conductor elongation (sag). Another effect of extreme weather is wind-induced conductor motion, referred to as Aeolian vibration and conductor galloping. Outdoor conditions are not only limited to environmental factors, but may also include line faults. Altogether, this hinders the efficient operation of the power grid, and may result in permanent damage to the network. Thus, a timely estimate of phase current, conductor elongation, and wind-induced motion can dramatically improve security of power grid and reduce outage times.
During recent years, many researchers have proposed methods for operation for state monitoring of overhead transmission lines. The methods involve both contact and non-contact based retrieval of spatial parameters and line current. In industry, non-contact measurement products such as Sagometer by Engineering Data Management have been recently commercialized, which measures sag in transmission lines using a camera as a sensor, and digital Image processing techniques. Another device is developed by Electric Research Power Institute which needs to be attached with live current carrying conductors to monitor conductor temperature, sag, current and vibration, as descripted in A. Phillips, “Evaluation of Instrumentation and Dynamic Thermal Ratings for Overhead Lines,” Electric Power Research Institute, Palo Alto, Calif., Tech, Rep., October 2013, in research, a group proposed the use of non-contact magnetic field sensors for estimation of spatial and electrical parameters of transmission line, as descripted in X. Sun, Q. Huang, Y. Hou, L. Jiang and P. W. T. Pong, “Noncontact Operation-State Monitoring Technology Based on Magnetic-Field Sensing for Overhead High-Voltage Transmission Lines,” in IEEE Transactions on Power Delivery, vol. 28, no. 4, pp. 2145-2153, October 2013. However, the method involves using a large number of sensing units, and computational expensive stochastic optimization techniques, which restrict the practical utilization of the approach.
A device disclosed in U.S. patent application publication no. 20120046799 has been presented which needs to be attached to the conductor and monitors temperature, inclination, voltage and current. The device includes a complete platform for instrumentation to send the measurements to the base station. However, the contact-based nature of the device limits its portability and incurs huge setup and maintenance costs.
An apparatus utilizing non-contact magnetic field sensing coils and a computerized method has been disclosed under U.S. Pat. No. 8,280,652. The device makes use of magnetic field measurements to calculate the distance between conductor and sensing elements, and then utilize the calculated distance for current load estimation. A number of sensing coils are placed on ground surface measuring the horizontal and vertical components of magnetic field radiated from phase conductors. However, the method only accounts for the sensor to conductor distance, and does not address the conductor elongation in neighboring spans where the sensing elements are deployed.
The present invention aims to overcome the deficiencies of prior art by providing a method for monitoring phase current and spatial parameters of overhead transmission lines with noncontact magnetic field sensor array. It can provide real time load monitoring as well as obtain spatial information of phase conductor positions, in rest and motion.